1. Field of the Invention
This invention relates to a recording method using a liquid composition which is capable of repetitively forming a coating film during flow of the liquid through a liquid flow passageway.
2. Description of Prior Art
Non-impact recording methods have recently drawn the attention of all concerned in view of their advantages; e.g., the noise which develops at the time of recording is so low as to be negligible. Of various types of the non-impact recording methods, the so-called "ink-jet recording method (the recording method by ejection of liquid through a nozzle)" is highly useful, according to which the recording operation can be effected on the so-called "plain paper" without subjecting it to a special treatment of image-fixing. Heretofore, various proposals for improving the ink jet recording system have been made and various ink jet recording devices have been embodied on the basis of such concepts, some of which have already been commercialized with improvements being incorporated, and others of which are still under way for their practical use.
As one example, the liquid jet recording method as disclosed in a laid-open German Patent Application (DOLS) No. 2843064 has a characteristic different from other liquid jet recording methods in that heat energy, i.e., the liquid droplet forming energy, acts on the liquid to be ejected to obtain the driving power for the discharge of the droplets.
According to this disclosed recording method, the liquid which has been subjected to the action of the heat energy undergoes a change in state together with a rapid increase in volume, and, by the force of action derived from the state change, the liquid droplets are discharged from an orifice (or orifices) at the tip end of the recording head, fly to a recording member, and adhere onto it to complete the recording.
The liquid jet recording method disclosed in the abovementioned DOLS No. 2843064 has such a characteristic that it is not only effectively applicable to the so-called "drop-on demand" recording method, but also enables the recording head to be readily made in a full line type, high density multi-orifice construction; hence, an image having high image resolution and image quality can be obtained at a high speed.
Thus, while the abovementioned liquid jet recording method possesses excellent characteristics, it is still necessary to improve its life in the repetitive operations of the recording head (i.e. service life) in those cases where the device is to be operated at a higher speed and for a longer operating period for recording images of high resolution and image quality.
The main factor which governs the service life of the recording head employed in the recording method as described above resides in the life of an electro-thermal transducer to be provided in the recording device as the heat energy generating element. That is, the recording head to be used in the above-described recording method has a construction as illustrated in FIG. 1 of the accompanying drawing, according to which the electro-thermal transducer 102 is generally constructed in such a manner that it may contact a liquid to be introduced thereinto, at a heat acting zone 107 where heat energy acts on the liquid, from a direction of an arrow A through a heat acting surface 109 as the energy acting zone. This construction enables the heat energy generated as the droplet forming energy to effectively and efficiently act on the heat acting zone 107.
For this purpose, in the case of using an ordinary recording liquid such as water as a liquid medium, it becomes necessary that electric leakage between the electrodes 113 and 114 through the recording liquid be prevented, and the upper layer 112 is formed at least on the heat generating resistive layer 111 at the heat generating zone 108 when manufacturing the head so as to protect the heat generating resistive layer 111 from the recording liquid, or thermal oxidation.
The principle of forming the flying droplets in the recording method using such recording head is as follows. When the electro-thermal transducer is subject to electric conduction as mentioned above, the recording liquid at the heat acting zone 107, which has received the action of the heat energy to form the droplets, undergoes a change of state accompanied by an abrupt increase in its volume, i.e., the recording liquid in the heat acting zone 107 is vaporized in an instant (on the order of a micro-second) to cause instantaneous bubbling and volume expansion at this heat acting zone 107. Then, when the electric conduction is disconnected, the liquid volume contracts instantaneously and the generated bubbles extinguish accordingly. The speed of this liquid volume contraction and bubble extinction is so high that it is substantially equal to, or slightly slower than, the speed in the abovementioned bubble generation and expansion.
As the result of an enormous amount of repeated experiments and careful studies by the present inventors, it has been discovered that, in the repetition of generation, expansion, contraction and extinction of the bubbles, the contraction and extinction of the bubbles which take place at the latter half of the repetitive process constitute, in particular, the main factor which governs the service life of the electro-thermal transducer.
That is to say, since the abovementioned process of the bubble contraction and extinction occurs at a very high speed, shock waves from these contractions and extinctions directly strike the heat acting surface 109. As a result, the heat acting surface 109 is subjected to impact by the shock waves every time the droplet discharging is repeated, and eventually it is damaged by the shock waves. In particular, the higher the frequency of a pulse signal to be applied for driving the electro-thermal transducer 108 (driving frequency) becomes (i.e., the more often the droplet forming operation is done to effect the high speed recording), or, the higher the level value of the pulse signal to be applied is made, the larger is the impact on the heat acting surface due to the shock waves. This constitutes the fundamental factor to curtail the service life of the electro-thermal transducer 102.
In addition, since a temperature difference on the heat acting surface 109 at the time of conduction and non-conduction of electricity thereto is remarkably large and such temperature difference occurs in a very brief period of time, a stress is imposed on the heat generating zone 108 due to such thermal factor, which is liable to cause a strain in the upper layer 112 whereby cracks tend to readily take place. This also constitutes one of the factors which governs the service life of the electro-thermal transducer due to its repetitive use.
As mentioned in the foregoing, in spite of the fact that the abovementioned recording method has the advantage of being able to mass-produce the device, particularly, the recording head of a high density multiorifice construction at a low manufacturing cost, using the most advanced IC (integrated circuit) fabrication technology of the present-day, it has an inherent problem still to be solved in its fundamental point of the droplet formation which constitutes the factor to largely govern the service life of the recording head.